1. Field of the Invention
The present invention relates to a transflective liquid crystal display (LCD) and more particularly, to a transflective LCD and corresponding manufacturing method capable of reducing misalignment (erroneous arrangement) of liquid crystals at an interface between a reflection portion and a transmission portion and improving a step coverage of the interface.
2. Description of the Related Art
Computer networks now allow users to connect and operate their laptop or other mobile device pretty much anywhere and at anytime. For example, users can connect to the Internet via a Web terminal, a mobile terminal, a personal digital assistance (PDA), etc. Further, the devices are also expected to display various information including still and moving images in color.
Also, the mobile devices are generally thin and light weight and tend to consume less power than standalone computing devices. In addition, a transmissive liquid crystal display (LCD) panel is generally used in the mobile devices. However, one problem with transmissive LCDs is that they require a backlight unit. That is, the power consumption of the backlight unit shortens the usage time of the mobile device and also adds to the thickness of the mobile device.
In an effort to overcome these problems, a reflective LCD has been proposed, which uses ambient light as a source of illumination. That is, the transmissive LCD including the backlight consumes about more than 70% of power than the reflective LOD. Further, because a backlight unit is not required in the reflective LCD, the mobile device can be made thinner and thus the weight of the device is also reduced.
However, the related art transmissive LCD has such low visibility that its color contrast is degraded by light reflection from a surface of a panel in bright environments. Further, the reflective LCD has a problem because natural light or ambient light such as an artificial light source does not always exist. That is, the reflective LCD may be used in an office or in a building in which external artificial light is provided, but cannot be used at night when natural light is not present.
Therefore, a transflective LCD has been developed that uses the advantages of the transmissive LCD and the reflective LCD. For example, FIG. 1 is an exploded perspective view showing a related art transflective color LCD. As shown in FIG. 1, the related art transflective LCD includes a second substrate 23 having a color filter 2 and a common electrode 18 (shown in FIG. 2) formed on a black matrix 44, and a first substrate 21 including a pixel electrode 3 having a transmissive portion (T) and reflective portions (R), a thin film transistor (TFT) 9, and array wirings 4 and 5. Further, liquid crystals 22 are filled between the second substrate 23 and the first substrate 21.
An operation of the transflective LCD with such a configuration will now be described with reference to FIG. 2, which is a sectional view of the related art transflective LCD. As shown in FIG. 2, the first substrate 21 having the TFT 9 and the second substrate 23 having the color filter 2 are disposed in a facing manner respectively on transparent substrates 11 and 16, and the liquid crystal layer 22 with liquid crystal injected thereto is interposed between the first and second substrates 22 and 23.
In addition, in the first substrate 21, the TFT 9, which is disposed at each pixel and applies or cuts off a signal voltage to or from the liquid crystal, is formed on the transparent substrate 11. Further, the TFT 9 includes a gate electrode 61 to which a scan signal is applied, and an active layer 62 including a semiconductor layer 62a made of amorphous silicon and activated according to the scan signal to form a channel and an ohmic contact layer 62b formed at both upper portions of the semiconductor layer 62a such that impurities are doped on the amorphous silicon. The TFT 9 also includes a gate insulating layer 60 that electrically separates the active layer 62 and the gate electrode 61, a source electrode 63 formed on the active layer 62 and receiving a data signal, and a drain electrode 64 applying the data signal input to the source electrode 63 to the pixel electrode 3 when the semiconductor layer 62a is activated.
Further, as shown, a passivation layer 27 for protecting the source electrode 63 and the drain electrode 64 is formed on the TFT 9 over the first substrate 21, and a contact hole 65 is formed at the passivation layer 27. Also, the common electrode 18 for applying voltage to the liquid crystal and the black matrix 44 for preventing light leakage are formed on the second substrate 28 corresponding to the region where the TFT 9 is formed.
In addition, a transparent electrode 17 is formed at a pixel region of each pixel, excluding the region where the TFT is formed, and is connected with the drain electrode 64 via the contact hole 65. A reflective electrode 12 made of metal with good reflectivity is also formed on the transparent electrode 17. Further, as shown, a portion of the reflective electrode 12 is removed to form the transmissive portion (T).
In addition, in a reflection mode of the transflective LCD, light incident from the exterior is reflected by the reflective portion (R) so as to be emitted to the exterior in a reflection mode, and in a transmission mode, light emitted from a backlight unit is transmitted through the transmissive portion (T) to thus display an image Further, as shown in FIG. 2, the passivation layer 27 at the region where the transmissive portion (T) is formed is removed to form a recess.
That is, the recess is formed to adjust an ON/OFF operation of the reflective portions (R) and the transmissive portion (T) and maximize the efficiency of the transmission mode. Further, in FIG. 2, a ratio of a cell gap (d2) of the transmissive portion (T) and (d1) of the reflective portions (R) is 2:1. That is, when the cell gap of the transmissive portion (T) is double the cell gap of the reflective portions (R) (i.e., d2=2d1), the highest transmission efficiency can be obtained at the reflective portions (R) and the transmissive portion (T).
However, because the TFT is formed on the first substrate 21, when the passivation layer is etched, the TFT is significantly affected that results in deficiencies and make the process complicated. In addition, after the etching process, the boundary surface of the passivation layer has a slope portion with a certain tilt Therefore, the liquid crystals aligned on the slope portion have a different arrangement from the liquid crystals aligned on the planar surface, which affect the arrangement of the liquid crystals formed on the planar surface adjacent to the slope portion.
This arrangement causes degradation of the contrast of a screen image in the transmission mode, and if the reflective portions extend to a portion of the flat transmissive portion (T) adjacent to the slope portion to avoid the degradation of contrast, an aperture ratio is reduced.